As a process for cresol production, there has been widely known a process in which cymene is oxygenated with oxygen gas and tertiary hydroperoxide of cymene is then decomposed into the desired cresols and acetone.
In this process, however, a primary hydroperoxide of cymene with an oxygenated methyl group is formed as a by-product in the oxygenation, together with the above tertiary hydroperoxide. The primary hydroperoxide is converted into isopropyl-phenol and formaldehyde through its decomposition. This formaldehyde may be condensed with the resulting cresols to form a resin, which will cause a decrease in the yield of cresols in this process.
To solve this problem, a process has been proposed, in which the decomposition of the primary hydroperoxide is stopped halfway to suppress the formation of formaldehyde, so that a yield decrease arising from the by-product can be prevented, and the remaining primary hydroperoxide is then hydrogenated into an alkylbenzene (see, e.g., JP-A 52-57130, JP-B 59-8246, JP-B 1-49248).
In this process, however, a portion of the primary hydroperoxide still decomposes. Therefore there will inevitably occur to a certain degree the side reaction between formaldehyde as the by-product and cresols as the major product, so that a loss of cresol yield will accompany the process. This process is not satisfactory with respect to the yield of cresols.
For the purpose of preventing the formation of formaldehyde, a process has been known, in which a mixture of the tertiary and primary hydroperoxides obtained by the oxygenation is subjected to hydrogenation below 50.degree. C. to decrease the content of primary hydroperoxide (see, e.g., JP-A 58-198468). In this process, a yield decrease arising from the formation of formaldehyde can be suppressed. However, the yield of cresols in this process cannot be satisfactory either. Further, the energy efficiency in the process is poor because the reaction temperature is 50.degree. C. or lower, and it cannot always be said that this process is satisfactory from an industrial point of view.